As a servo control of a synchronous motor, a vector control that separates a current in a field magnetic flux direction (d-axis) of the motor and a direction perpendicular to the field magnetic flux direction (q-axis) and performs current control for the d axis and the q-axis is generally performed. In the vector control, it is necessary to detect magnetic pole positions in order to generate a torque effectively.
A linear motor is often used in combination with an incremental encoder that cannot detect an absolute position of the motor at the time of power activation. Since the incremental encoder can detect only a relative position, it is necessary to detect an initial magnetic pole position. If accuracy of the initial magnetic pole position detection is poor, an axial misalignment phenomenon that a dq-axis (a dm-pm axis) of an actual motor and a dq-axis (a dc-qc axis) for control are misaligned occurs. Accordingly, an adverse effect, such as degradation of torque control accuracy or a reduction in a maximum torque, occurs.
When an absolute encoder is used, it is not necessary to detect the initial magnetic pole position since an absolute position can be detected. If mounting accuracy is low, axial misalignment also occurs.
A technique for estimating offset of the magnetic pole position when the encoder is mounted on the synchronous motor is an example of the related art, and is disclosed in Patent Document 1 (JP-A-2001-204190).
Patent Document 1 discloses an error adjusting device that adjusts an error based on an initial magnetic pole position estimation value of a synchronous motor that includes a unit for calculating an initial magnetic pole position of a rotator. Here, a command torque current among a two-phase command current is set to zero and a command magnetic flux current is set to a predetermined finite repetitive waveform. Then, an angular acceleration is calculated based on a detection velocity. An occurrence torque is estimated based on information, such as the command magnetic flux current, a detection velocity, the angular acceleration, and an inertia, viscous friction, and a friction torque of the motor according to a motor motion equation. A torque current is estimated by dividing the estimated torque by a torque constant. An initial magnetic pole position is estimated based on the command magnetic flux current and the estimated torque current. Finally, the estimation result is displayed.
As another example of the related art that estimates a magnetic pole position of a rotator in position-sensorless control of a salient pole type synchronous motor and performs control based on the estimated magnetic pole position value, a motor control device is disclosed in Patent Document 2 (JP-A-10-323099).
Patent Document 2 discloses the motor control device that has a unit for applying an AC current signal for estimation or an AC voltage signal for estimation in one axial direction of an orthogonal two-axis coordinate system and estimating a magnetic pole position of the synchronous motor based on a current or voltage in the other axial direction of the orthogonal two-axis coordinate system. The magnetic pole position estimation unit estimates the magnetic pole position using a current or voltage value, which is detected at a timing of a predetermined phase with respect to the AC current signal for estimation or the AC voltage signal for estimation.
In the initial magnetic pole position estimation device disclosed in Patent Document 1, an offset angle of an initial magnetic pole position when the encoder is mounted on the AC synchronous motor is accurately estimated according to an initial magnetic pole estimation equation and the estimated offset angle is displayed. Accordingly, the initial magnetic pole position can be correctly controlled. However, since estimation can be carried out only when a command torque current (q-axis current command iqc*) is zero, the initial magnetic pole position estimation device cannot perform estimation during a normal operation, such as velocity control.
In the initial magnetic pole position estimation device disclosed in Patent Document 1, a series of works for displaying an axial misalignment angle, mounting the encoder again, and then estimating the axial misalignment angle must be repeatedly performed. Accordingly, there is a problem in that an inefficient work occurs.
In the initial magnetic pole position estimation device disclosed in Patent Document 1, a division is used for a process of estimating the axial misalignment angle. Therefore, there is a problem in that robustness against noise, friction variation, disturbance load, and/or the like is low.
In the initial magnetic pole position estimation device disclosed in Patent Document 1, parameters, such as inertia or friction, are required in order to estimate the axial misalignment angle. Accordingly, there is a problem in that estimation accuracy is significantly low when accurate parameters are not found.
In the motor control device disclosed in Patent Document 2, a magnetic pole position of the synchronous motor can be simply estimated by detecting a current, which flows according to the signal for estimation, in the other axial direction of the orthogonal two-axis coordinate system at a predetermined phase, and performing a multiplication operation on the detected current. However, the motor control device cannot detect an actual velocity shift or position movement since it does not include a velocity detecting unit or a position detecting unit and cannot employ velocity feedback information. Accordingly, the disclosed motor control device has a problem in that accuracy of magnetic pole position estimation is rarely improved.
The motor control device disclosed in Patent Document 2 has a problem in that it is rarely applied to a motor not having an electrical saliency or having a small electrical saliency, since it uses the electrical saliency.
In the motor control device disclosed in Patent Document 2, only a current feedback can be used since an electrically closed property is used (a current command cannot be used). Accordingly, the disclosed motor control device has a problem in that it is affected by current detection noise.
In the motor control device disclosed in Patent Document 2, a superimposed signal and a detection signal do not have the same phase. Accordingly, there is a problem in that a sequence is complicated since a solution for detecting the superimposed signal and the detection signal at specific phase timings, a solution for calculating a peak value or a shift rate, and so on are required.
The invention has been made in order to solve the above-described problems, and it is a first object of the invention to provide a motor control device that can estimate an initial magnetic pole position even during a normal operation, such as velocity control or the like, in vector control of a synchronous motor by a simple configuration.
It is a second object of the invention to provide a motor control device that does not use a division to estimate an axial misalignment value.
It is a third object of the invention to provide a motor control device that can estimate an initial magnetic pole position even, without using motor parameters.
It is a fourth object of the invention to provide a motor control device that can obtain data required to estimate an axial misalignment angle, without using a complex sequence for obtaining a data acquisition timing.